Some engine trouble

L

Lt.Col.Vortex

Joined
Jul 22, 2012
Messages
752
So I'm stumped and I need a third or forth opinion on some engine trouble I'm having. The engine is a Kohler CV20 Command Pro, vertical shaft, VTwin, single barrel carb. If you want further details just ask me.

The engine is mounted to a 2004 Scag Cub ZTR mower and of late its been giving me troubles and its now affecting my work. Since its a V engine, its running 2 magnetos and their run in series. The last one in this series is the cylinder thats acting up.

Problem 1: When throttling up rabidly, then engine cuts out altogether. I have to slowly walk the throttle up.

Problem 2:When starting, engaging blades or anything that requires a load drawn, the #2 piston (I'm calling it...the one with the last in series magneto) cuts out and wont come back until the load is gone.

Any suggestions?? I wont tell you what my conclusions are as to not sway your judgments. I've spent 2 days thinking and working on this but nothing final yet. All I can really do is troubleshoot and clean/visual inspection, it is not my equipment so I do no replacing of parts or diagnosing....I just take care of and use the stuff.
 
Maybe, that would suggest a bag magneto on one side but it wouldn't explain why both sides drop out when throttling up rapidly.

You may be right, there may be more than one problem...its just that this all come on at once.
 
have u tried playing with the carb give it more fuel maybe during the rapid throttle it leans out n shuts off
 
I tried bumping the choke when I draw a load, but it doesn't help. I could give it more fuel, but that doesn't explain the one piston cutting out. This is a single barrel carb, meaning air and fuel get mixed and head off to both pistons through the same line....one carb feeds both cylinders.
 
Is it points, or solid state ignition? I've used the "quick-fix" aftermarket solid state ignition chips on other magneto engines, and it worked. (I think the brand was Lazer-ignition, or something) My guess is either timing, or something is keeping the sparks from flying. That said, I'm kinda talking out my a$$ as its been a long time since I played in a small engine.
 
It sounds like a fuel issue to me,does this have a fuel pump or is it gravity feed?Either way the first thing that I would check is the fuel flow but if it cuts out when you open the throttle quickly,it sounds like there might be dirt in the carb that's not letting it transition from the low speed circuit to the high speed circuit smoothly.I don't imagine this has an adjustable carb on it either,back in the "old days" an issue like that might have been rectified by opening the low speed jet 1/8 or 1/4 turn.
 
sykes3170 said:
Bad valves on number 2?
Click to expand...

This maybe close...

Does this Kohler engine have over head valves? my dad has a riding mower and it got to be 4 to 6 years old and went to running like crap. tinkered and tuned and what ended up being the problem in this case was the the valves loosened up, the ends of the valves and the rocker arms wore off and got out of spec and needed to be reset.

if you have had the engine apart check rings if broke or burnt and the sleeve for excessive wear. are gaskets good? or leaking and sucking air somewhere. sometimes you can get a motor running and take a can of starting fluid and spray around where parts meet like the head and cy;inder meet and manifold s joint, don't spray it oin the intake that will just make the engine race, but spray one of these junctions and the engine revs up you have found a leak sucking air and need a new gasket or maybe a new part if warped or cracked. if it has a fuel pump not gravity feed may need to rebuild it or get a new one, had this problem on an old Wisconsin motor on a trencher.. has the carburator been looks at, maybe be plugged up or need a new daiphramkit installed. sometimes electrical gets weak and runs good until you get a load on it then the points, coil, condensor weaken up and won't pull good.

not much help but stuff to look at, got to tinker with it

not cheap to work on these kinds of motors, a friend has one who does lawn care and the oil plug vibrated out and new motor cost about 60% of the mower.

be patient, stay calm and don't get mad, you can get this.
 
be patient, stay calm and don't get mad, you can get this.
Click to expand...

lol, cant do that...got stuck in a ditch today because the engine cut out and I slid in.

gadgetgeek:Electric starting with solenoid shift starter, 12 Volt Electric Ring Gear Type, Key and Solenoid Operated Interlock...copied from the mower PDF. I wont lie, I'm not good with the more technical details of electronics. I know just enough to get myself in trouble and barely enough to get myself out. I dont think its starter or timing issue because the spark cuts out when initial load is draw and at almost rhythmic intervals afterwards ( after the load is drawn and is kept drawing steadily ( blades engaged and cutting grass ), the #2 piston kicks back in and cuts out in almost a predictable pattern I if the load is kept constant )).

beau5278: I know its not a fuel problem because when the engine is running and it skips, I smell unburned fuel. That and this is a single barrel carb, if one cylinder acts up the other will too.

sykes & omniviking: Maybe but its hard to tell. I'm only allowed to clean and do visual inspection. I'd love to tear this thing apart, but its not mine. The engine is new, it was rebuilt/replaced ( rent remember what was dont to it ) in the last 8 years. But the previous operator ran this thing into the dirt. I'm sure there are several problem with the mower and the engine, but right now I need the problem at hand fixed. It may be a conglomeration of issues, but its right now beyond my expertise...I'd recommend replacing parts at this point and hope I get it right. I know about whats wrong and about what to fix, but I dont know any definite.

Thanks guys for your help, even though it may seem like I shot your theories down. I'm settling with the fact that its a failing magneto(s) and bad plugs ( the engine has overheated several times in the past...which my have caused more problems ) ...that is until it return from the shop some time next week..the I'll let you know what the 'pros' said the problem was.
 
Magnetos are normally very reliable. you can check the strength of the spark by pulling off the lead when the engine is running (wear a rubber glove or hold with dry cloth) and see how far the spark will jump. It should jump a gap of well over 1/2", if not, there is a fault somewhere. First port of call is the carbon core plug lead. bypass it with ordinary copper wire temporarily and see if it runs better. If so, fit a new lead.
 
Sounds like it could be two different problems. Problem one sounds like a fuel/carb issue. It's either leaning the motor out or dumping too much fuel in when you rapidly throttle it. If the motor has gone eight years since its been rebuilt, ethanol content in the fuel could have caused havoc with the fuel system(seals, gaskets, lines...) Problem two sounds more like a timing/ignition issue. Sounds like you know where to start with that can of worms. If I read your post right, eight years is a pretty good run for any small engine in a commercial setting.
 
I've had some experience with solenoids in industrial electric applications. The first rule of troubleshooting motor controls is:

Blame The Solenoid!

My guess is that your "solenoid shift starter" is faulting under sudden load. It would be really good to find a circuit diagram, and if you can, you may find that your solenoid has two poles, one for each magneto.

If that's not it, I would get a volt/ohmeter and work your way down the chain, checking voltage and resistance at the poles of you solenoids. Time-consuming, yes, but necessary.
 
Blame The Solenoid!
Click to expand...
lol, yep, learning that :)


I do think the spark was rather weak, so the plugs and magnetos will be changed out. As for the assumed fuel issue, I'm not 100% confidant that it has a fuel problem...but thats my ego speaking. When I got this mower, the frame had 2920 hours on it ( the engine only had a grand or so hours on it ), and it was rode hard and put up wet by the previous owner. I got it singing again rather well, it started on the second rotation, it never had power issues, I got it to stop overheating and got it to run cooler, I fixed a ton of small issues ( like spitting oil from random places ), and now at hour 3000 its wanting to show its age. So yes there could be a carb issue ( I am very religious about CLEAN gas...no freeking ethanol ), but you never know. The issues started rather suddenly and progressed rather rapidly. I did a full physical and cleaning on the engine and frame recently, so its now a clean mower with issues :)

I do have a wiring diagram ( thank you Scag for at least having good customer support ) and I've pored over that thing quite a lot. I could word down the line and find the exact problem, but I'm fairly confident on what the problem is so I'll just have parts changed. If I'm wrong its no big deal, 99% of the parts are going bad or are about to go bad on it anyways.
 
omniviking said:
This maybe close...

Does this Kohler engine have over head valves? my dad has a riding mower and it got to be 4 to 6 years old and went to running like crap. tinkered and tuned and what ended up being the problem in this case was the the valves loosened up, the ends of the valves and the rocker arms wore off and got out of spec and needed to be reset.
Click to expand...

This would be my best guess. I would first check the easy stuff, plugs, carb, magneto. But in the back of my mind, this would be the number one suspect.

if you have had the engine apart check rings if broke or burnt and the sleeve for excessive wear. are gaskets good? or leaking and sucking air somewhere...
Click to expand...

Another potential culprit, but I would not like to do the tear down to fix it.
 
My thoughts are its a too much fuel issue when the high speed cuts in... Like having the choke on under load and temperature...... doesn't work, runs too rich which will give you unburnt fuel .... This is then either too much fuel or not enough air. Either would give too rich a mix... Maybe a mouse nest in the intake on the second cylinder?

ANother way you get this symptom of cutting out under load is with poor spark/igniton. Have you put properly gapped new plugs in?
 
Rapt_up said:
My thoughts are its a too much fuel issue when the high speed cuts in... Like having the choke on under load and temperature...... doesn't work, runs too rich which will give you unburnt fuel .... This is then either too much fuel or not enough air. Either would give too rich a mix... Maybe a mouse nest in the intake on the second cylinder?

ANother way you get this symptom of cutting out under load is with poor spark/igniton. Have you put properly gapped new plugs in?
Click to expand...


I'm doubtful the fuel only because I've never had a problem yet with it and I've spit cleaned every part of the carb. I thought it might be to much fuel on the higher end, but I couldn't explain why it all of a sudden started dumping more fuel like that. There where no air blockages to cause greater fuel suction, and all other carb/air parts where clean...so I directed my attention to electrical.

The shop 'experts' that are repairing the thing ( I'm not allowed to do any repairs, its not my equipment ) said it sounds like week spark/bad magnetos. The magneto spacing looked good, so I'll settle for week spark till I figure out otherwise.
 
OK, got the mower back from the shop. 70% of the problem was a crapped out head gasket on the #2 side (side giving me trouble). This engine is covered in so much useless crap that you can barely see the block, so unless i took the thing part I would have had no way of knowing this. But they replaced it and tightened the head bolts (supposedly a few where loose). They also claimed that there was water in the carb bowl. I call BS on this because I drained and cleaned the carb less than a week before. I suspect they are trying to pin the problem on random things, but I know better. Like said 70% of the problem is fixed, the thing still cuts out, but only on engaging the blades now. I ran through 2 foot tall thick grass today and it ran just fine, so I'm sticking to my guns about weak spark. One day it'll be fixed, but since the boss is cheap and the mower will cut without to much trouble, I'm stuck with it for now.
 
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